The present invention relates to a data collection system for automatically reading electric, water or gas meters in remote places to collect data as to electric, water or gas quantities consumed for a predetermined period.
A prior art system which is related to the present invention will be described with reference to FIG. 1. A central or data collection station has a circuit 1 for controlling relays for selecting counters. For instance, a control signal is transmitted through counter-selection lines C.sub.R1 and C.sub.R2 to energize a coil of a relay R.sub.1 to close a contact R.sub.1b. Thereafter, a counter-reading control circuit 2 is operated to impress a predetermined voltage on a transmission line L.sub.1 so that a current flows through the line L.sub.1, a least-significant-digit contact A.sub.11 of a counter M.sub.1, a counter resister R.sub.1, the relay contact R.sub.1b, a common transmission line L.sub.0 and a detecting resistor R.sub.D. Counter resistors R.sub.0 through R.sub.9 of the counter M.sub.1 have different values so that a value of the current flowing through the above circuit changes depending upon the position of the counter contact A.sub.11 and is detected in terms of a voltage drop across the detecting resistor R.sub.D by a voltage detecting circuit 3. In this case, the least-significant-digit of the counter M.sub.1 is 1. In like manner, the control circuit 2 impresses a predetermined voltage on a transmission line L.sub.2 to read the next least-significant digit or second digit. Since a second-digit contact A.sub.21 is connected to a resistor R.sub.0, the second digit is 0. In like manner, the third digit and the fourth digit or most significant digit may be read out and displayed by a display device 4. In this case, reading of the counter M.sub.1 results 0901.
In the prior art system of the type described, each of a plurality of transmission lines has stray capacitance so that when the control circuit 2 impresses a predetermined voltage on, for instance, the transmission line L.sub.1, the latter is charged to stray capacitance C.sub.1 within a relatively very short time as the transmission line L.sub.1 has a relatively small resistance. After this stray capacitance C.sub.1 has been charged, the common transmission line L.sub.0 is charged through the counter resistor R.sub.1 to a stray capacitance C.sub.0. In general, the counter resistors R.sub.0 through R.sub.9 have high values ranging from 1K ohms to 10K ohms. Because the common transmission line L.sub.0 is charged through one of these high resistance it takes a considerably long time before a voltage drop corresponding to that across the counter resistor R.sub.1 is derived across the detecting resistor R.sub.D. As a result, the control circuit 2 must be operated with a relatively long switching time sufficient to permit the charging of the common transmission line L.sub.0 to C.sub.0 so that high-speed data collection cannot be accomplished.